Semiconductor scaling is slowing down because of difficulties of device manufacturing below logic 7nm
node generation. Various lithography candidates which include ArF immersion with resolution enhancement
technology (like Inversed Lithography technology), Extreme Ultra Violet lithography and Nano Imprint
lithography are being developed to address the situation. In such advanced lithography, shot counts of mask
patterns are estimated to increase explosively in critical layers, and then it is hoped that multi beam mask
writer (MBMW) is released to handle them within realistic write time. However, ArF immersion technology
with multiple patterning will continue to be a mainstream lithography solution for most of the layers. Then,
the shot counts in less critical layers are estimated to be stable because of the limitation of resolution in ArF
immersion technology. Therefore, single beam mask writer (SBMW) can play an important role for mask
production still, relative to MBMW. Also the demand of SBMW seems actually strong for the logic 7nm
node. To realize this, we have developed a new SBMW, EBM-9500 for mask fabrication in this generation. A
newly introduced electron beam source enables higher current density of 1200A/cm2. Heating effect
correction function has also been newly introduced to satisfy the requirements for both pattern accuracy and
throughput. In this paper, we will report the configuration and performance of EBM-9500.
In the half pitch (hp) 16nm generation, the shot count on a mask is expected to become bipolar. The multi-patterning
technology in lithography seems to maintain the shot count around 300G shots instead of increase in the number of
masks needed for one layer. However, as a result of mask multiplication, the better positional accuracy would be
required especially in Mask-to-Mask overlay. On the other hand, in complex OPC, the shot count on a mask is expected
to exceed 1T shots.
In addition, regardless of the shot count forecast, the resist sensitivity needs to be lower to reduce the shot noise effect so
as to get better LER. In other words, slow resist would appear on main stream, in near future. Hence, such trend would
result in longer write time than that of the previous generations. At the same time, most mask makers request masks to
be written within 24 hours. Thus, a faster mask writer with better writing accuracy than those of previous generations is
With this background, a new electron beam mask writing system, EBM- 9000, has been developed to satisfy such
requirements of the hp 16nm generation. The development of EBM-9000 has focused on improving throughput for
larger shot counts and improving the writing accuracy.
EBM-9000 equipped with new features such as new electron optics, high current density (800A/cm2) and high speed deflection control has been developed for the 11nm technology node(tn) (half pitch (hp) 16nm). Also in parallel of aggressive introduction of new technologies, EBM-9000 inherits the 50kV variable shaped electron beam / vector scan architecture, continuous stage motion and VSB-12 data format handling from the preceding EBM series to maintain high reliability accepted by many customers. This paper will report our technical challenges and results obtained through the development.
To reduce down time associated with routine cathode replacement we developed a turret-type electron gun
for our electron beam mask writer, EBM-8000. This enables us to exchange cathodes without venting the gun
to atmosphere, thereby reducing the downtime for cathode replacement by 80% compared to conventional
Two key elements were considered in developing the turret-type electron gun: reducing fluctuation in beam
current, and eliminating discharge sources.
Reducing fluctuation in beam current is one of the most important elements because it has an impact to
critical CD accuracy. In EBM-8000, the current fluctuation must be 0.1% (3s) or less to attain the CD
accuracy specification. We will explain how the beam stability is realized.
Special treatment to eliminate discharge sources is necessary to realize long-term stability of the electron
gun. We devised a conditioning sequence which repeatedly increases and decreases the voltage applied to the
barrel in N2 atmosphere. This conditioning sequence allowed us to dramatically decrease the probability of
discharges, allowing us to achieve long-term stability operation.
Many lithography candidates, such as ArF immersion lithography with double-patterning/double-exposure techniques,
EUV lithography and nano-imprint lithography, show promising capability for 22-nm half-pitch generation lithography.
ArF immersion lithography with double-patterning/double-exposure techniques remains the leading choice as other
techniques still lack the conclusive evidence as the practical solution for actual production. Each of the prospective
lithography techniques at 22-nm half-pitch generation requires masks with improved accuracy and increased complexity.
We have developed a new electron beam mask writer, EBM-8000, as the tool for mask production of 22-nm half-pitch
generation and for mask development of 16nm half-pitch generation, which is necessary for the practical application of
these promising lithography technologies.
The development of EBM-8000 was focused on increasing throughput and improving beam positioning accuracy. Three
new major features of the tool are: new electron gun with higher brightness to achieve current density of 400 A/cm2,
high speed DAC amplifier to accurately position the beam with shorter settling time, and additional temperature control
to reduce the beam drift.
The improved image placement accuracy and repeatability, and higher throughput of EBM-8000 have been confirmed
by actual writing tests with our in-house tool.
In order to comply with the demanding technology requirements for 45 nm half pitch (HP) node (32 nm technology
node), Nuflare Technology Inc. (NFT) has developed Electron-beam mask writing equipment, EBM-6000, with
increased current density (70A/cm2), while its other primary features basically remain unchanged, namely 50 kV
acceleration voltage, Variable Shaped Beam (VSB)/vector scan, like its predecessors [1-5]. In addition, new
functionalities and capabilities such as astigmatism correction in subfield, optimized variable stage speed control,
electron gun with multiple cathodes (Turret electron gun), and optimized data handling system have been
employed to improve writing accuracy, throughput, and up-time. VSB-12 is the standard input data format for
EBM-6000, and as optional features to be selected by users, direct input function for VSB-11 and CREF-flatpoly
are offered as well.
In this paper, the new features and capabilities of EBM-6000 together with supporting technologies are reported to
solidly prove the viability of EBM-6000 for 45 nm HP node.
The keys to precision x-ray mask fabrication are the EB mask writer and the process of writing on a thin membrane. This paper concerns the delineation performance for 100 kV EB writing on x-ray membrane mask. We installed and evaluated an advanced EB mask writer, the EB-X3, which features an accelerating voltage of 100 kV and a 5-axes laser interferometer stage employing a laser measurement system with a resolution of 0.6 nm for high resolution and accuracy. The stable 100 kV EB has a good resolution around 50 nm and a beam address of 1 nm, which provide a repeatability of mark detection within 4 nm. As a result, an absolute image placement accuracy within 15 nm was obtained for 1G-bit level ULSI patterns. In addition, the combination of 100 kV EB and membrane process was found to reduce proximity effects. By several improvements including higher-order height correction and membrane process refinement, the final target of an absolute image placement error within 10 nm and a CD accuracy within 8 nm should be achieved in FY2000.
This paper describes a 100-kV thermal-emission electron gun developed for the X-ray mask writer, EB-X2, which employs a variable-shaped electron beam with a beam edge resolution of 20 nm. The optimized design of the EB-X2 electron optical system requires that the electron gun have crossover diameters of 50 micrometers and an optical length of less than 100 mm. So the crossover diameters of the gun were accurately calculated with an electron ray tracing program, and a gun with the required crossover diameters and optical length was designed. The gun was constructed, and the crossover diameters were measured. The measured values agree well with the calculated ones, and this confirms that the gun is suitable for use in the EB-X2 electron optical system.
This paper describes a new design for a field emission electron gun immersed in a magnetic- lens field. Its low aberration yields both a high brightness and a high emittance. A single-pole- like magnetic lens made a water-cooled pipe coil produces a magnetic flux density of 0.28 T at the emitter tip. The spherical aberration of the gun, as calculated by an electron ray tracing program, is only 1/3 that of a conventional gun with a magnetic lens. A prototype of the gun was constructed using a zirconium-oxide/tungsten thermal-field emitter. The measured crossover diameters agree with those calculated by the ray tracing program, confirming that the aberration is very low.